RD&D-Programme 2004 - SKB

Conclusions in RD&D 2001 and its review
SKI points out the importance of the influence of saline groundwater on the hydraulic properties
of the backfill. Future changes in the salinity of the groundwater must also be taken into
account, see also Kasam’s viewpoints in section 18.2.21.
Newfound knowledge since RD&D 2001
In principle, the backfill works in the same way as the buffer, see section 17.2.15. Saline
groundwater will, however, have a greater relative influence on the physical properties of
the backfill, since the density of the montmorillonite fraction is lower in the backfill. Current
compaction technology for backfill materials in a deposition tunnel does not provide sufficiently
high montmorillonite density to meet the safety margins under sea water conditions.
Programme
See section 17.2.15. For backfill materials, the development work will be focused on emplacement
technique to increase the montmorillonite density, see section 18.1.6, and testing of
different clay materials.
18.2.14 Ion exchange/sorption
Ion exchange from sodium to calcium leads to similar effects as high salinity in the groundwater
(see section 17.2.16) in a backfill material with a low content of swelling clay, i.e. the pore
geometry in the backfill material is altered and the backfill risks losing its swelling and sealing
properties.
Conclusions in RD&D 2001 and its review
SKI maintains that SKB should evaluate what saline groundwaters mean for the repository.
Newfound knowledge since RD&D 2001
See section 17.2.16.
Programme
See section 17.2.16.
18.2.15 Montmorillonite transformation
What is said about montmorillonite transformation in the buffer is largely applicable to the
backfill as well, see section 17.2.17. The boundary conditions exhibit certain differences,
however. The temperature in the backfill is lower and less iron is available, which would lead to
slower transformation. On the other hand, the density may be lower and the quantity of cement
may be higher, which could lead to more rapid transformation.
Conclusions in RD&D 2001 and its review
In Kasam’s opinion, SKB should set a limit on how much potassium the crushed rock may
contain.
Newfound knowledge since RD&D 2001
See section 17.2.17.
RD&D-Programme 2004 237